1. Field of the Invention
The present invention relates to a data communication device and method for a mobile communication system. More particularly, the invention relates to a device and method for communicating control information for a data communication service using a dedicated control channel in a mobile communication system which provides multimedia data communication service.
2. Description of the Related Art
At present, mobile communication systems using CDMA (Code Division Multiple Access) technology have become increasingly widespread. Conventional CDMA mobile communication systems based on the TIA/EIA IS-95 CDMA standard, transmit control signals for call processing multiplexed with data on a traffic channel carrying voice information. The traffic channel has a fixed frame length of 20 ms. Control signals may be transmitted as messages on dedicated frames by a blank-and-burst technique, or on a (frame shared with main user traffic by a dim-and-burst technique.
CDMA communication systems that provide multimedia services including packet data service as well as voice service are coming of age. These new systems may separate channels for the voice and data services to flexibly allocate the channels at the users"" request. To this end, the CDMA mobile communication system includes a voice traffic channel (or fundamental channel) and a packet traffic channel (or supplemental channel).
Conventionally, for the data service through the fundamental channel and the supplemental channel, the CDMA mobile communication system typically maintains use of the fundamental channel to transmit the control signal, even in a state where there is no communication between the base station and mobile station. This results in a waste of channel resources, thereby limiting radio capacity. In addition, the conventional CDMA mobile communication system uses the fixed single frame length of 20 ms without regard to the size of a message to be transmitted, which may cause low throughput and traffic delays.
It is, therefore, an object of the present invention to provide a dedicated control channel structure capable of efficiently communicating a control message between a base station and a mobile station, a call control message of an upper layer and a control message for connection of a packet traffic channel, by providing a dedicated control channel by which the mobile station can exclusively communicate the control signal to the base station in a CDMA mobile communication system, and a method for operating the same.
It is another object of the present invention to provide a device and method for generating and communicating a control message having a variable frame length according to the size of the control message in a CDMA mobile communication system using a dedicated control channel.
It is still another object of the present invention to provide a device and method for adaptively and intermittently communicating a control message on a dedicated control channel according to the presence/absence of the control message in a mobile communication system using the dedicated control channel.
It is a further object of the present invention to provide a frame data processing device and method, in which a reception device receives frame data transmitted in a discontinuous transmission mode, detects an energy level of the received frame data and determines presence/absence of an effective frame so as to process the frame data according to the determination.
It is yet another object of the present invention to provide a frame data processing device and method, in which a receiver receives frame data transmitted in a discontinuous transmission mode, detects an energy level of the received frame data and determines presence/absence of an effective frame, so as to process the received frame data according to a frame detection result and an error detection result.
To achieve the above and other objects, in one aspect of the invention there is a CDMA system-for transmitting messages having at least two different frame lengths. The system includes: a controller that determines a frame length of a message to be transmitted and outputs a frame select signal corresponding to the determined frame length; at least one message generator for generating frame data of the message to be transmitted according to the frame select signal; and a transmitter for spreading the frame data and transmitting the spread frame data through a dedicated control channel.
The message generator may include a Cyclic Redundancy Check (CRC) generator for generating CRC bits for the message in the frame length determined according to the frame select signal and adding the CRC bits to the message, a tail bit generator for generating tail bits and adding the generated tail bits to an output of the CRC generator, a channel encoder for encoding the tail bit-added frame data with a predetermined encoding rate; and an interleaver for interleaving the encoded message by a unit of the frame length determined according to the frame select signal.
The system may include as many message generators as the number of frame lengths of the message to be transmitted. The respective message generators generate the frame data in the corresponding frame length.
The controller may be adapted to generate an output control signal to implement a discontinuous transmission mode when there is no message to transmit. The transmitter preferably includes a path controller for controlling an output of the dedicated control channel in response to the output control signal. The path controller may comprise a gain controller whose output gain becomes zero in response to the output control signal.
In accordance with another aspect of the present invention, there is provided a CDMA system that receives messages having at least two different frame lengths. This system includes: a despreader for despreading a signal received through a dedicated control channel; a first message receiver for deinterleaving and decoding the despread signal in a first frame length to output a first message, and detecting a first CRC corresponding to the decoded signal; a second message receiver for deinterleaving and decoding the despread signal in a second frame length to output a second message, and detecting a second CRC corresponding to the decoded signal; and a controller for selecting one of the first and second messages according to first and second CRC detection results by the first and second message receivers.
The controller may include a frame decider for analyzing the first and second CRC detection results to decide a frame length of the received message and output a frame length decision signal, and a selector for selecting one of the decoded signals output from the first and second message receivers according to the frame decision signal.
In accordance with still another aspect of the present invention, a CDMA system that receives messages having at least two different frame lengths includes: a despreader for despreading a signal received through a dedicated control channel; a frame detector for detecting energy of the despread signal in first and second frame lengths and outputting first and second frame detection signals according to the detection results; a first message receiver for deinterleaving and decoding the despread signal in the first frame length to output a first message; a second message receiver for deinterleaving and decoding the despread signal in the second frame length to output a second message; and a controller for selecting one of the first and second messages according to the first and second detection results.
The frame detector may include first and second frame detectors. The first frame detector has as a reference value a minimum energy value of a 5 ms effective frame and compares an energy value of the received frame message with the minimum energy value of the 5 ms effective frame to generate a first frame detection signal when the energy value of the received frame message is higher than the minimum energy value of the 5 ms effective frame. The second frame detector has as a reference value a minimum energy value of a 20 ms effective frame and compares an energy value of the received frame message with the minimum energy value of the 20 ms effective frame to generate a second frame detection signal when the energy value of the received frame message is higher than the minimum energy value of the 20 ms effective frame.
In accordance with a further aspect of the present invention, a CDMA system that receives messages having at least two different frame lengths includes: a despreader for despreading a signal received through a dedicated control channel; a first frame detector for detecting an energy of the despread signal in a first frame length to output a first frame detection signal according to the detection result; a second frame detector for detecting energy of the despread signal in a second frame length to output a second frame detection signal according to the detection result; a first message receiver for deinterleaving and decoding the despread signal in the first frame length to output a first message and detecting a first CRC corresponding to the decoded signal to output a first CRC detection signal; a second message receiver for deinterleaving and decoding the despread signal in the second frame length to output a second message and detecting a second CRC corresponding to the decoded signal to output a second CRC detection signal; and a controller for selecting one of the first and second messages according to the first and second frame detection results and the first and second CRC detection results.
The controller includes a frame decider and a selector. The frame decider analyzes the first and second CRC detection signals and the first and second frame detection signals, judges the received frame to have the second frame length when the second CRC detection signal and the second frame detection signal are received, judges the received frame to have the first frame length when the first CRC detection signal and the first frame detection signal are received, and judges the received frame to be an error frame when other CRC and frame detection signals are received. The selector outputs a corresponding one of the decoded signals output from the first and second message receivers upon receiving one of first and second frame length decision signals, and controls an output of the decoded signal upon reception of an error frame decision signal. In addition, the frame decider determines that no frame is received when none of the first and second frame detection signals and none of the first and second CRC detection signals are received.